Some circuits are designed to provide a source of voltage or current to serve as a reference for other circuits, including analog-to-digital converters (ADCs) and digital-to-analog converters (DACs). Thus, the accuracy of the reference often determines the accuracy of the circuitry so supplied. As greater numbers of measurement systems are deployed in hostile environments with a variety of temperatures, the demand for apparatus and methods that provide precision reference signals in such environments will increase. For these and other reasons there is a need for apparatus and methods that provide a substantially stable reference signal over a wide temperature range.